The Human Neostriatum Shows Compartmentalization of Neuropeptide Gene Expression in Dorsal and Ventral Regions: an in Situ Hybridization Histochemical Analysis

Expression of neuropeptide messenger RNAs in striatal neurons was studied in post mortem human brain tissue by the use of in situ hybridization histochemistry. Clusters of cells expressing high levels of prodynorphin messenger RNA, and less strikingly, preprotachykinin messenger RNA, were prominent in the caudate nucleus and were present but less pronounced in the putamen. Proenkephalin and prosomatostatin messenger RNA-containing cells were more homogeneously distributed throughout the striatum, though the latter were much sparser. The four neuropeptide messenger RNA patterns in the nucleus accumbens were rather homogeneous compared with the dorsal striatum. Of these, prodynorphin messenger RNA showed a higher level of expression per cell in the nucleus accumbens relative to the dorsal striatum. The relationship of neuropeptide-containing cell clusters to the striosomal organization was characterized by looking at the register of these markers with patterns of low acetylcholinesterase activity and dense mu opiate receptor binding. In the caudate and putamen, clusters of cells expressing high levels of dynorphin and preprotachykinin messenger RNAs were clearly in register with the striosomes. The accumbens was defined by high prodynorphin messenger RNA levels, both low and high levels of acetylcholinesterase staining, and very low to absent mu opiate receptor binding. The distribution of high-expressing prodynorphin messenger RNA-containing cells--to the patch compartment and throughout the entire ventral striatum/nucleus accumbens region--defines the limbic domain of the neostriatum and suggests particular relevance to human striatal organization and function, because the distribution of this opioid neuropeptide is considerably more compartmentalized in human than in non-human species.